This invention relates to improvements in spindle motors for rotatably supporting and driving one or more memory storage disks in computer disk drives. More particularly, this invention relates to an improved disk drive spindle motor having a compact arrangement for mounting Hall sensors used in motor timing and directional control, while substantially isolating computer disks from changing magnetic fields associated with the Hall sensors.
Disk drive units in general are known in the art for use in modern microcomputers such as personal and desk top computers and the like. In one popular form, such disk drive units comprise a so-called Winchester drive having one or more memory storage disks supported in a stack by a compact spindle motor within a substantially sealed disk drive housing. The spindle motor rotatably drives the disks in close proximity with one or more electromagnetic transducers which are appropriately controlled to read or write data on prepared disk surfaces. Such disk drive units, sometimes refer to as "hard" or "fixed" disks, are normally available as a compact package with the sealed housing assembled on a rigid chassis together with a circuit board carrying the requisite drive electronics to interface with other components of a computer system.
In one common form, spindle motors for disk drive units have comprised small dc motors designed for rapid disk acceleration to a substantially constant operating speed, typically about 3,600 rpm. Such motors commonly include solid state commutation components such as Hall sensors mounted in close association with a timing magnet which rotates with the computer disks. In operation, the Hall sensors respond to changing magnetic fields attributable to the timing magnet to generate control pulses used to regulate spindle motor direction and speed. For efficient operation, these changing magnetic fields must have a minimum strength to insure reliable triggering of the Hall sensors. However, the field strength normally decreases in response to increased operating temperatures. Accordingly, to insure accurate triggering of the sensors throughout a normal range of operating temperatures, a relatively high strength or high energy timing magnet is required. Unfortunately, the use of a high energy timing magnet can result in stray magnetic flux which can adversely affect data storage or retrieval on one or more of the computer disks, particularly at inner tracks on the disks. This data interference problem can be particularly significant in modern "micro" disk drives of the type used in personal or lap top computers, such as so-called 3.5 inch disk drives and the like.
The object of the present invention is to provide an improved spindle motor for a computer disk drive, wherein the spindle motor has an improved yet highly compact mounting arrangement for Hall sensors in association with a relatively high energy timing magnet, while substantially isolating computer disks from the magnet flux field associated with the timing magnet.